Formation and Stabilization of Noble Metal Nanoparticles

The kinetics of homogeneous and heterogeneous nucleation processes of metal (Ag, Pd) nanoparticles was studied by UV-VIS spectrometry. Silver nanoparticles were prepared in aqueous solution by homogeneous nucleation using poly(vinylpyrrolidone) (PVP) and sodium citrate as sterical stabilizers. Reduction was ensured by adding hydroquinone. According to kinetic functions, reduction is an autocatalytic process: a slow, continuous nucleation is followed by a fast, autocatalytic growth. The presence of polymer inhibits nucleation and retards the rate of particle growth. Formation of palladium nanoparticles was investigated in aqueous medium via reduction by hydrazine, using PVP and the clay mineral hectorite as stabilizers. Effects of the polymer and concentration of silicate and palladium ions on the particle formation rate were analyzed. The rate of reduction is decreased by increasing amounts of stabilizing agents and increased by increasing concentrations of precursor ions. The kinetics of heterogeneous nucleation was determined based on the adsorption of the palladium species at the clay mineral particles and the viscosity of the hectorite dispersion.